IL-17 and Th17 cells have an important role in the host response to fungal infections. In the current study, we examined the role of IL-17 in a murine model of Aspergillus and Fusarium infections of the cornea, which are a major cause of blindness and visual impairment worldwide. C57BL/6 mice immunized by intratracheal or subcutaneous routes. Mice immunized by either route demonstrated rapid fungal clearance and significantly reduced corneal disease compared with unimmunized, infected mice which severe corneal opacity and a persistent fungal presence. Intracellular flow cytometry showed development of fungal-specific Th1 and Th17 cells in the spleen following immunization, which were selectively recruited to the cornea after infection (Th17 cells at 48h, and Th1 cells at 72h). Neutralization of IL-17 following immunization, or infection of IL-17-/- mice inhibited the protective phenotype, whereas IFN-? neutralization had no effect. A discrete population of IL-17 producing neutrophils was detected in the corneas 24h after infection corneas of immunized, but not unimmunized mice, and were detected in the spleen and bone marrow. Further, neutrophil depletion impaired IL-17 production at this time and blocked protective immunity. IL-17 producing neutrophils produced elevated ROS and had increased capacity to kill hyphae in vitro, indicating that this population of cells has an important role in regulating fungal infectio. Quantitative PCR of the FACS sorted IL-17 neutrophils from the cornea, spleen and bone marrow showed IL-17 transcripts, indicating de novo synthesis. Further, naive bone marrow neutrophils expressed IL-17 RNA when incubated with splenocyte supernatants from immunized mice, and expression was ablated in the presence of both anti-IL-6 and anti-IL-23. Conversely, stimulation with both IL-16 and IL-23, but not with single Abs stimulated IL-17 expression. Together, these data indicate that IL-17 producing neutrophils are generated by IL-6 and IL-23 in immunized mice, and are recruited to fungal infected corneas, resulting in rapid fungal clearance possibly due to elevated production of reactive oxygen species or interactions with Th17 cells. These findings show a role for IL-17, Th17, and IL-17 producing neutrophils in regulating fungal infections. In the proposed experiments I will determine the relative contribution of Th17 cells and IL-17 producing cells in protective immunity in fungal keratitis. ) PUBLIC HEALTH RELEVANCE: Project narrative: Fungal keratitis is one of the leading causes of corneal ulcers, visual impairment, and blindness. In many cases the current anti-fungal treatments for this infection are not adequate in resolving the disease. However, the results from the proposed studies could lead to proper regulation and novel therapies for this debilitating infection.